Internal combustion engines and drivetrains operate under a wide range of temperatures including low temperature stop-and-go service, as well as high temperature conditions produced by continuous high speed driving. Sludges or insolubles are produced under some operating conditions and dispersants are added to the lubricating oil so that potentially insoluble materials remain dispersed in the oil.
It is known to employ nitrogen-containing dispersants in the formulation of crankcase and drivetrain lubricating oil compositions. Many of the known dispersants are based on the reaction of an alkenyl succinic acid or anhydride with an amine or polyamine to produce an alkenyl succinimide.
Flexible engine seals are used in assembling internal combustion engines and drivetrains to prevent leakage of lubricants at locations where moving parts, such as crankcase shafts, extend outside the engine block. Accordingly, qualification tests have been established whereby the effect of a lubricant composition on seal-type materials is measured under a particular set of controlled laboratory bench test conditions. One such test measures the compatibility of the lubricant with a specified fluoroelastomer, namely, VITON fluoroelastomer. This is a special test material that has been developed for use in the fluoroelastomer seal tests. The material is intended to simulate the proprietary seal materials in actual use by the original equipment manufacturers. Thus the commercial reality is that the lubricant must exhibit good performance in the test in order to achieve acceptance in the marketplace.
U.S. Pat. No. 5,080,815 to Fenoglio et al describes dispersants having improved compatibility toward the fluorohydrocarbon-containing elastomer. Those dispersants are formed by reacting a hydrocarbyl-substituted dicarboxylic acid compound such as a hydrocarbyl-substituted dicarboxylic acid anhydride with aminoguanidine or a basic salt thereof in a ratio of about 1.4 to about 2.2 moles of aminoguanidine or basic salt thereof per mole of hydrocarbyl-substituted dicarboxylic acid compound.
U.S. Pat. No. 4,908,145 to Fenoglio describes dispersants for lubricating oils that are also compatible with the fluorohydrocarbon elastomer. These dispersants are enriched in alkyl-bis-3-amino-1,2,4-triazole (e.g., polybutenyl-bis-3-amino-1,3,4-triazoles) and are formed by reacting an alkyl-substituted dicarboxylic acid compound, such as a polyisobutenyl succinic acid compound, with a basic salt of aminoguanidine at a ratio of from about 1.6 to about 2 moles of aminoguanidine compound per mole of the alkyl-substituted dicarboxylic acid compound.
Both of the foregoing patents show in Table II thereof that dispersants made in accordance with their teachings exhibited good compatibility with VITON fluoroelastomer in the Caterpillar VITON Compatibility Test. These patents also show results of spot dispersancy bench tests which indicate that a product prepared by reacting one mole of aminoguanidine bicarbonate per mole of polyisobutenyl succinic anhydride was relatively ineffective as a dispersant.